The invention describes the use of Near IR spectroscopy to determine the amount of biodiesel in a conventional diesel by collecting the NIR spectrum, applying a mathematical function to the absorbance spectrum, and using a multivariate regression model to predict the biodiesel content. It is shown that multiple sources of biodiesel, and multiple sources of conventional diesel can be used in a single regression model. The predicted result can be used to control an automated or manual blending process at a petroleum refinery, product terminal, or truck loading facility.
Biodiesel is an alternative fuel source derived from soy, animal fat, vegetable oil, or restaurant oil waste. It is produced in a transesterifiction reaction using the oil or fat and an alcohol such as methanol to produce a methyl ester. In the near future, it is expected some states are going to mandate the addition of biodiesel to conventional diesel refined from petroleum crude oil. Simple, rapid analytical techniques will be needed to measure the amount of biodiesel added to a conventional fuel in the blending process. Spectroscopy, more specifically Near Infrared (NIR) spectroscopy, is well suited to make this determination.
Near IR has been used effectively to quantitatively monitor the physical properties of hydrocarbon fuels. Several patents are cited. The technique is non-destructive to the sample, multiple properties can be predicted from a single spectrum, and it has been shown it can be placed on-line to monitor a process or blender stream in real-time.
In literature cited, Knothe describes the use of Near IR to quantitatively monitor the transesterification biodiesel reaction. Using regions in the NIR near 6005 cm−1 and 4425-4430 cm−1 it is possible to quantify the amount of vegetable oil residual in the biodiesel as the reaction progresses. Previously, gas chromatography (GC) had been used to monitor the reaction, but NIR is faster and the use of in-line sample probes makes it more convenient.
Knothe also describes a method in the literature to predict biodiesel content in a conventional diesel using the raw NIR spectral absorption and a principal component regression model. The NIR regions described included a region near 6005 cm-1 and 4425 cm-1-4430 cm-1. Knothe used only a single source of soy methyl ester in the experiment.
Currently, several commercially available instruments operating in the mid-IR region can determine biodiesel content in a conventional diesel.